4.2. Subjective mode

This section and the next describe the
subjective mode of measuring colony strength and are thus best suited for
collecting response variables while the field experiment is in progress. The
gist of the method is the use of human observers who visually estimate the
surface area of a comb covered by a target; bees, brood, honey, pollen, etc., and
if necessary convert comb surface to target-appropriate units, i.e. bees, cm2,
or cells. The syntheses in sections 4 and 5 draw from the work of Burgett and
Burikam (1985) and derivative papers from North America (Skinner et al., 2001, Delaplane et al., 2005, 2010), Imdorf et al. (1987) and Imdorf and Gerig
(2001) from Europe, and Gris (2002) and Guzman-Novoa et al. (2011) from Central America.

1. Visual estimates of bees on combs will vary according
to time of day and bee foraging activity. For this reason it is important to
control for this effect – either by limiting observations to a narrow time
window on successive days, randomly assigning time of inspection such that day
effect is equitably and randomly distributed across treatments, or closing hive
entrances in the early morning until bees are counted.

2. Estimates should be carried out by no fewer than two
human observers, preferably each with a dedicated secretary who writes down
numbers, or each fitted with an audio recorder.

3. A colony is opened and combs of bees sequentially
removed. Each observer looks at one side of a comb, visually estimates the
percentage of the comb surface covered by bees, and records the number with the
secretary or audio recorder. It is convenient to label frames 1-X, with each
side indicated A or B. For beginners it is advisable to “calibrate the
individual” with estimates made by an experienced observer. Observers describe
the process as a kind of mental “resorting” the bees, such that the bees are
imaginatively moved into a contiguous mass on the comb surface, at which point
the reader estimates the percentage surface of the comb they cover. It is
important to visually sort the bees into a contiguous mass that approximates
their density if the frame were fully covered because the bee densities given
in Table 2 (1.23 – 1.77 bees per cm2) apply to combs at full
carrying capacity.

4. Investigators can use the values in Table 2 or
calculate the comb side surface area unique to their equipment. Fig. 8 is a
screenshot of an Excel datasheet demonstrating the conversion of raw data from
two observers into colony bee population. There are two fictional colonies,
each with 5 North American deep frames, each with two sides. Columns D and E
show the respective visual estimates of two observers for percentage comb
surface covered by bees, and column F is the mean of the two. Column G converts
the mean percentage surface covered by bees into area (cm2) covered
by bees, using the surface area for one side of a North American deep frame
from Table 2 (880 cm2). Column H converts cm2 bees to
number of bees with the appropriate bee density (1.38 bees / cm2).
Finally, rows 12 and 23 sum the bees of each frame and side to yield colony bee
population.

5. If investigators use colonies with different sized
supers and frames it will be necessary to adjust calculations for the one-side
surface area unique to each comb type. Bee density at full carrying capacity is
consistent within North America or Europe, so it should be adequate to pick a
density value from Table 2 that best fits one’s local situation.